1. Field of the Invention
The present invention relates to adsorbents made from active metals dispersed on inert porous supports, such as alumina, silica aluminosilicates, zeolites, clay and the like effective for removing low level elemental mercury from hydrocarbons.
2. Discussion of Background and Material Information
The present invention is based on the discovery that elemental mercury in naphtha can pass through a steam cracker somewhat unscathed and can attack the aluminum bundles of a down-stream cold box resulting in the failure thereof. In addition to the economics associated with the failure of the cold box, a collapse of the cold box would also pose environmental problems.
Various attempts have been made in the prior art to remove mercury contaminants from hydrocarbon streams. For example, it is known that elemental mercury can be removed from a hydrocarbon stream using a packed bed of metal particles, such as copper, silver, aluminum and zinc. In so doing, the mercury forms an amalgam with the active metals and remains on the particle surface.
The previous attempts to remove mercury, however, have not been found to be successful in preventing elemental mercury in naphtha from passing through the steam cracker. First, the particles of metal are not porous so that only the outer surface is available for a mercury reaction and adsorption. Consequently, the column size and amount of metal required to treat high volumes of naphtha are somewhat impractical. Second, the outer surface of the active metals, such as aluminum, copper, and zinc is typically covered with a layer of metal oxides. Thus, an acid-wash pre-treatment is normally needed to remove the oxide layer and activate the metal particles before use for this purpose. The latter treatment, however, imposes extra difficulties on safety, operations, and waste disposal. For the sulfide approach, its operations include precipitation, filtering and handling of a wet filter cake which are inefficient.
U.S. Pat. No. 4,417,626, DOMTAR Inc., discloses the use of sodium sulfide to remove mercury from wastewater.
J.P. 62-68,584, KOKAI Tokyo Koho, uses arsenic sulfite to remove mercury from wastewater.
U.S. Pat. No. 3,704,875, PENNWALT Corp., discusses the use of active metal particles, including zinc and aluminum, to remove mercury from aqueous streams such as wastewater and other industrial wash effluents.
U.S. Pat. No. 3,883,426, ETUDES ET PROCEDES d'ASSAINISSEMENT PURATOR, also discusses the use of active metal particles including zinc and aluminum to remove mercury from aqueous streams, such as wastewater and other industrial wash effluents.
Sulfides, such as sodium sulfide, have also been proposed to precipitate the mercury from the hydrocarbon liquid.
Related to the foregoing, other techniques have been proposed for the removal of mercury from liquids and gases. An example of technology of mercury removal from liquids and gases is outlined in the Encyclopedia of Chemical Technology, 3d Edition, Vol. 15, pp. 168-169 (1981).
It has also been proposed to adsorb mercury on high surface area substrates, such as activated carbon.
French Patent No. 2,310,795, INSTITUTE FRANCAIS DU PETROLE, discloses the removal of mercury from gases and liquids using an adsorbent mass of metal on a ceramic support. The method disclosed involves contacting the gas or liquid with an adsorbent mass containing a) SiO.sub.2, Al.sub.2 O.sub.3 silica-alumina, a silicate, and aluminate or an aluminosilicates support, and b) one or more metals which form alloys with mercury. The adsorbent mass is disclosed as having a specific surface area of greater than 40 m.sup.2 /g, i.e. 40-250 m.sup.2 /g, and the metal in the mass is present as crystallites having an average diameter of less than about 400 Angstroms, and preferably less than 100 Angstroms. The support is disclosed as preferably being Al.sub.2 O.sub.3 and the preferred metal is Ag or a mixture Ag with Au, Ni or Cu. The adsorption mass may also contain ThO.sub.2 or MgO. It is disclosed that the activation of the adsorption mass and/or its regeneration are effected by heating in the presence of a like hydrocarbon and optionally steam. The support is disclosed as preferably being in the form of 1-10 mm diameter balls, such as extrudates or pellets. Optionally, the support may be mixed with the active phase and then formed into pellets. The adsorbent metal is used in amounts of 200 ppm--20%, and more preferably 0.05-1% for Au and 0.1-5% for Ag or Cu. It is disclosed, however, that other metals may be present in amounts within the range of 0-20% and preferably 0.01-10%. It is also disclosed that regeneration is effected by heating at 200.degree.-500.degree. C., and preferably 320.degree.-420.degree. C. in a current of inert or reducing gas.
NL 7613-998, Institute Francais Du Petrole, discloses the use of dispersed sulfided metal on an inorganic carrier to remove mercury from gases or liquids by contacting the fluid with a fixed bed of an adsorbent comprising Cu sulfide on SiO.sub.2, Al.sub.2 O.sub.3, SiO.sub.2 --Al.sub.2 O.sub.3, silicate, aluminate or alumina silicate support in the treatment of natural gas, liquified natural gas, and electrolytically produced H.sub.2.
SU 633,565, KAZEA UNIVERSITY, is directed to the removal of mercury from industrial air by using a silica gel adsorbent containing silver oxide. The adsorbent is disclosed as being prepared by impregnating silica gel with silver nitrate and calcining.
JP 52-105,578, MITSUI MINING & SME, is directed to the removal trace mercury from exhaust gases by adsorption in columns packed with noble metal-supporting, nonmetallic fibers, e.g. of quartz.
DE 3,026,430, NIPPON KOKAN K.K., discloses the removal of resolved heavy metals from liquids by adsorption of metals on steelwork slag, which is disclosed as being particularly suitable for removing mercury and the like, from waste water.
JP 53-73,859 discloses the use of ferrous salts on activated carbon for the removal of mercury ions from effluent.
JP 49-74,195, SUMITOMO CHEMICAL CO., LTD., discloses the use of an activated carbon impregnated with copper for mercury removal from gas.
The following patents relate to mercury removal over activated carbons.
U.S. Pat. No. 3,755,989, UNION CARBIDE CORPORATION, is directed to mercury removal from a gas stream by feeding the stream to a carbon adsorbent bed.
French Patent No. 2 206 843, SHOWA DENKO K.K., is directed to removal of mercury from gases by adsorption on active carbon treated with sulfuric acid.
JP 5 2053-793, SUMITOMO METAL MINI K.K., is directed to the removal of trace mercury from sulfuric acid by conversion to bromide or iodide followed by adsorption on activated carbon.
DL 107-890, BEILING H., is directed to removing mercury from effluent waters by adsorption on active carbon and ion exchange resin and elusion.
SU 640-750, FEDOROVSKAYA L. F., is directed to removal of mercury from industrial waste gas by adsorption on activated carbon in the presence of chlorine for high adsorption capacity.
DE 160-802-A, CHEM WERK BUNA VEB, is directed to mercury removal from gas by adsorption on sulfur-containing active carbon.
SU 1161-157-A, SECONDARY RESOURCES, is directed to the removal of mercury vapor from gases by adsorption on activated charcoal treated with vinyl chloride oligomers.
However, removal of mercury contaminants from the hydrocarbon stream is a problem which has been solved by the present invention, as described in more detail hereinafter, in a manner which is believed to be novel and unobvious relative to what has been taught by the prior art.